BACKGROUND: Chronic obstructive pulmonary disease (COPD) is predominantly caused by cigarette smoking and is considered a worldwide preventable chronic illness. Smoking cessation is considered the primary intervention for disease management and nurses should play a major role in assisting patients to stop smoking. Currently there is a lack of professional consensus on how cessation interventions should be evaluated. The vast array of biochemical markers reported in the literature can be confusing and can make the comparisons of results difficult. OBJECTIVE: To validate self-report data on smoking with exhaled carbon monoxide in patients with chronic obstructive pulmonary disease over twelve months.DESIGN: We performed a secondary analysis of a previously published randomized controlled trial evaluating nursing interventions to assist respiratory patients to stop smoking.SETTING: Northern Ireland's Regional Respiratory Centre.PARTICIPANTS: A total of 91 cigarette smokers attending secondary care for the treatment for COPD participated in the study.METHOD: Self-reported smoking status and cigarettes smoked per day were compared to exhaled carbon monoxide readings at baseline, 2, 3, 6, 9 and 12 months. The cut-off value of ≤10 ppm was used to identify non-smokers. The p-values are based on Pearson's correlation coefficient and Kappa Coefficient as appropriate.RESULTS: Findings suggest self-reported smoking status and cigarette consumption amongst patients with chronic obstructive pulmonary disease was highly consistent with exhaled carbon monoxide results (p = 0.001-0.003).CONCLUSION: The majority of patients with chronic obstructive pulmonary disease reliably report their cigarette consumption.